Knock Through & RSJ Steel Beam London
Knocking through two cramped rooms into one open-plan space is the single most transformative thing you can do to a London terrace or flat. The reception and dining room become one bright, sociable space; the kitchen opens to the garden. But almost every wall worth removing is load-bearing, and that means a steel beam — an RSJ — designed to carry what the wall used to.
- Fixed Written Quotes
- Guaranteed in Writing
- Free On-Site Survey
Knock Through & RSJ Steel Beam London
Knocking through two cramped rooms into one open-plan space is the single most transformative thing you can do to a London terrace or flat. The reception and dining room become one bright, sociable space; the kitchen opens to the garden. But almost every wall worth removing is load-bearing, and that means a steel beam — an RSJ — designed to carry what the wall used to.
The work that matters is invisible once it is finished: the structural engineer’s calculations, the padstones the beam bears onto, the building control inspections, and the fire and acoustic detailing where the opening affects an escape route or a neighbour. Skip any of it and you inherit a sagging lintel and a problem at resale.
We deliver knock-throughs end to end: engineer’s design, building control, the RSJ installed on padstones, then plastering, flooring and decoration so the join disappears. One team, one fixed price, one completion certificate.
What's Included
- Structural engineer calculations for RSJ sizing and padstones
- Building control notification, inspections and completion certificate
- Temporary propping (acrow props and strongboys) during the works
- Steel beam supplied, treated and installed on engineered padstones
- Fire protection and boxing-in of the steel where required
- Plastering, flooring, skirting and making good both sides
- Spoil removal and clearance under licensed waste transfer
- Fixed written quote and workmanship guarantee in writing
What It Costs in London
These are guide prices to help you budget. We give you a fixed, written quote after a free on-site survey — no call-out charge and no surprises later.
| Work | Guide Price |
|---|---|
| Simple opening (small non-load-bearing or modest span)Forming the opening and making good | £800 – £1,200 |
| Internal wall removal with RSJLoad-bearing wall, steel beam, full reinstatement | £1,800 – £4,500 |
| Solid-brick Victorian wall openingHeavier wall, more propping and making good | £1,000 – £1,600 |
| Large opening / bi-fold or wide spanWider beam, additional support | £1,400 – £2,000 |
| Structural engineer calculationsRSJ sizing and padstone design | £300 – £600 |
Guide prices only — every job is confirmed with a fixed written quote after a free survey. Prices exclude VAT where applicable; your written quote states the VAT position clearly.
Our Process, Step by Step
Free survey & feasibility
We confirm whether the wall is load-bearing, measure the span and check what sits above it. You get a fixed, itemised quote covering the steel, the engineer, building control and making good.
Engineer design & building control
A structural engineer calculates the RSJ size and the padstones it bears onto, and we submit the building control notification so inspections are booked around the programme.
Prop, beam & padstones
We install temporary support (acrow props and strongboys), cut the opening, set the padstones and lift the RSJ into place, then transfer the load onto the new beam under building control inspection.
Making good & sign-off
The beam is boxed in and fire-protected where required, the opening is plastered, floors and skirtings are reinstated, and building control signs off. You receive the completion certificate.
Frequently Asked Questions
A simple opening in a modest wall costs £800–£1,200. Removing a load-bearing internal wall with an RSJ typically runs £1,800–£4,500 depending on span and making good. Solid-brick Victorian walls sit around £1,000–£1,600, and large openings for bi-fold doors £1,400–£2,000. Structural engineer calculations are £300–£600. We quote a fixed price after a free survey.
If the wall is load-bearing — carrying the floor or wall above — then yes, you need an RSJ or another engineered support sized by a structural engineer. Only genuinely non-load-bearing partitions can come out without a beam, and we confirm which you have at survey by checking joist direction and what sits above the wall.
Yes. Removing or forming an opening in a load-bearing wall is a structural alteration requiring building regulations approval. The engineer’s calculations are submitted, building control inspects the beam and bearings, and a completion certificate is issued — which you will need for resale and remortgage. We handle the whole process.
A padstone is a high-strength concrete or engineered block that spreads the steel beam’s load into the brickwork at each end. Without correctly sized padstones the beam can crush the masonry beneath it over time. The structural engineer specifies the padstone size and bearing length, and building control inspects them before the load is transferred.
A typical load-bearing knock-through with an RSJ takes about 1–2 weeks on site, including propping, beam installation, building control inspection and making good. Simple openings are quicker. The engineer’s design adds a short lead time before work starts, which we arrange in parallel with ordering the steel.
Property Refurbishment
Complete property refurbishment in London, managed end to end. One contractor for strip-out, building works, M&E, plastering, joinery and decoration.
View service Cost GuideKnock Through Cost in London: RSJ & Steel Beam Price Guide 2026
A knock through in London costs £1,800–£4,500, or £7,000+ for complex spans. See RSJ steel beam costs, what's included and how to get a fixed quote.
Read the guideAcross Every London Borough
We form open-plan knock-throughs and install RSJ steel beams in terraces, semis and flats across every London borough — from Wandsworth and Hammersmith to Hackney and Camden.
Get Your Free Survey & Fixed Written Quote
Book a free on-site survey and we'll return an itemised, fixed-price quote in writing — anywhere in London. No call-out charge, no surprises later.
- Same-day callback
- Fixed price, in writing
- Guaranteed workmanship